1. Field of the Invention
The present invention relates to light-emitting diodes and manufacture methods thereof, and more particularly to group III nitride semiconductor vertical type light-emitting diodes (VLED) and its manufacture methods.
2. Description of the Related Art
Light-emitting diode (LED) is a semiconductor component part that can emit visible light produced as a result of the recombination of electrons and holes in the semiconductor structure. A different wavelength of light can be emitted by adjusting the band gap of the semiconductor layer structure.
FIG. 1 is a schematic view illustrating a conventional vertical-type light-emitting diode 100. The VLED 100 mainly comprises a n-type semiconductor layer 106, a light-emitting layer 108, and a p-type semiconductor layer 110, mainly made of group III-nitride semiconductor compounds. Such layer structure is grown on a substrate (not shown), which is then removed from the final VLED 100.
During operation, light emitted from the light-emitting layer 108 spreads in all directions. For improving light extraction, a reflective layer 111 is usually formed below the p-type semiconductor layer 110 for redirecting light emitted by the light-emitting layer 108. In addition, the conventional VLED 100 may also incorporate a metal layer 112 for increasing current distribution during operation and enhance heat dissipation.
Further, a p-type electrode 114 is formed under the metal layer 112, and a n-type electrode 116 is formed above the n-type semiconductor layer 116. Operation of VLED 100 is performed by generating a current flow between the two electrodes.
Even with the reflective layer 111, some of the light from the light-emitting layer 108 still cannot exit the VLED 100 owing to inner absorption, refraction or interference. To improve light extraction, Taiwan Patent Application Publication No. 200847462 entitled “Vertical light emitting diode device structure”, the disclosure of which is incorporated herein by reference, proposes a layer structure in which a “spacer” is interposed between the light-emitting layer 108 and the p-type semiconductor layer 110. The material of the spacer is a compound having chemical formula AlxGayInzN, wherein 0≦x, y, z≦1. Such approach requires to modify the epitaxy deposition of the group III-nitride semiconductor compounds, which may adversely affect the active layers of the VLED 100.
Therefore, there is a need for a VLED structure and manufacture method that can increase extraction efficiency and address the foregoing issues.